Rotatable, oblique-viewing stereoendoscopes are known in the art. A stereoendoscope acquires stereoscopic images. An oblique-viewing stereoendoscope includes a prism for folding the Field of View (FOV) of the endoscope. That is, the prism changes the Direction of View (DOV) of the endoscope from a zero angle DOV to an oblique angle DOV. A rotatable oblique-viewing stereoendoscope can be rotated about the longitudinal axis thereof for changing the FOV of the endoscope. It is noted that the parallax between the images acquired by the stereoendoscope should be maintained horizontally leveled for allowing stereopsis.
Reference is now made to U.S. Pat. No. 5,689,365, issued to Takahashi, and entitled “Stereoscopic-Vision Endoscope”. This publication relates to a stereoscopic-vision endoscope having an objective optical system and a rear optical system. The objective optical system is positioned infront of the rear optical system. The objective optical system has a single optical axis and includes an oblique-vision observation optical system (e.g., a prism folding the Field of View—FOV—of the endoscope relative to the tube axis). The rear optical system has a plurality of optical axes. The front and rear optical systems can be turned relative to each other, thereby changing the tilted Direction of View (DOV) of the endoscope.
It is noted that the objective optical system includes a negative power, diverging, lens (e.g., lens 14b of FIG. 7) located in front of the folding FOV prism (e.g., prism 14c of FIG. 7). The front negative lens does not perform reimaging the pupils distally to the prism. The front diverging lens is directed at decreasing beam wandering inside this folding prism. That is, light beams arriving at the diverging lens from wide angles are diverged such that they are reflected from the folding prism, and do not enter the endoscope to smaller angles such that they are reflected twice, without vignetting, inside FOV folding prism. Thereby, the negative lens limits the FOV of the endoscope.
Reference is now made to U.S. Pat. No. 5,743,847, issued to Nakamura et al., and entitled “Stereoscopic Endoscope Having Image Transmitting Optical-System and Pupil Dividing Unit That Are Axially Movable with Respect to Each Other”. This publication relates to a rigid stereoscopic endoscope including an inserting portion, an operational holding portion and a pupil dividing means. The inserting portion is coupled with the operational holding portion. The operational holding portion and the pupil dividing means are rotatable relative to each other. The inserting portion incorporates an objective lens consisting of a plurality of lenses including a prism for oblique-vision observation, and a relay lens portion consisting of a plurality of lens groups from its distal end side. It is noted that the rigid stereoscopic endoscope includes a negative power lens positioned in front of (i.e., distally to) the oblique-vision prism (as can be seen in FIG. 2). As mentioned above, the front negative lens does not perform reimaging the pupils distally to the prism and limits the FOV of the endoscope.
Reference is now made to U.S. Pat. No. 5,825,534, issued to Strahle, and entitled “Stereoendoscope Having a Folded Sight Line”. This publication relates to a stereoendoscope having a sight line folded relative to the tube axis. The endoscope includes an endoscope tube and a viewing component. The endoscope tube and the viewing component are rotatable with respect to each other so that the line of sight can be changed. The endoscope tube includes distal front optics, including a deflecting prism, a negative refractive power component and a proximal component having a positive refractive power. The deflecting prism is mounted between the negative refractive power component and the proximal positive refractive power component. As mentioned above, a front negative refractive power component does not perform reimaging the pupils distally to the prism and limits the FOV of the endoscope.
Reference is now made to U.S. Pat. No. 5,588,948, issued to Takahashi et al., and entitled “Stereoscopic Endoscope”. This publication relates to a stereoscopic endoscope including an inserting section, and a pupil dividing device, rotatable with respect to each other. The inserting section includes an objective lens system and an image transmission device coaxially arranged with the objective lens system. The objective lens system includes folding prism and a negative lens positioned in front of the prism (as can be seen, for example, in FIGS. 7, 13a and 15). As mentioned above, a front negative refractive power component does not perform reimaging the pupils distally to the prism and limits the FOV of the endoscope.